http://3cbzkrvakrpetjjppdwzbzqrlkmzatjs7jbyazap5gwutj32gcltjpqd.onion
For example, I could take a bus and get off after tapping my card, but I would have no way to determine how much this journey cost. When you tap in, the maximum fare amount gets deducted. When you tap out, the balance amount gets refunded (if it’s a shorter journey than the maximum fare one).